Microsoft issued a rare out-of-cycle emergency patch fort a sderious vulnerability in its Internet Explorer (IE) Web browser late yesterday.

The critical hole in IE that the new patch plugs is very similar — at least in the way it works — to the one in the popular Firefox browser which was also patched yesterday. The IE vulnerability was first revealed by third party security researchers earlier this month and MS came under increasing pressure from users and critics to get a fix to users.

In both cases, the vulnerability would have allowed cyber crooks to download and install malware on unsuspecting users computers with no other user action than simply visiting a booby-trapped Web site.

The patch applies not only to the current version of IE (7), but to previous versions including IE 5.01, IE 6, and IE 6 Service Pack 1.

If you don’t have Auto Updates enabled on your computer, take a moment sometime today to visit the Windows Update site via the convenient link in your Windows Start menu and get the patch. You can also get more information about the patch and download it directly from the MS Update Web site.